This invention relates to novel light-sensitive condensation products of aromatic diazonium salts, processes for preparation thereof, and to light-sensitive reproduction materials, which comprise a support having a reproduction layer thereon containing at least one of the novel light-sensitive products.
It is known to use light-sensitive aromatic diazonium compounds for sensitizing reproduction materials which are useful for the production of single copies, printing plates, screen printing, color proofing foils and other applications in the reproduction arts.
U.S. Pat. Nos. 3,867,147; 3,679,419 and 3,849,392 relating to mixed diazo condensates, the contents of which are hereby incorporated by reference, describe an advance overcoming disadvantages of prior art diazo compounds and reproductive layers made therefrom.
Diazonium compounds conventionally known as light-sensitive agents for making light-sensitive lithographic printing plates can be divided into two kinds depending on their specific properties. That is, one kind is a diazonium compound capable of being decomposed by exposure into an oleophilic material and the other kind is a diazo compound capable of being converted by exposure into an alkali-soluble substance. When a composition containing the former kind of compound is applied on a hydrophilic support and the support is exposed to light through a transparent or translucent negative original, only the exposed portions are rendered hydrophobic and organophilic, that is, water repellent and ink receptive, and the unexposed portions can easily be removed with water or a phosphate solution whereby a negative image can be obtained. Such a system is described in detail in U.S. Pat. No. 2,714,066. On the other hand, when a composition containing the latter kind of compound is dissolved in an organic solvent, applied to a hydrophilic support and after exposure is developed by an alkaline solution, the exposed portions are dissolved out to provide a positive image. Such a system is described in detail in U.S. Pat. Nos. 3,046,122 and 3,046,123.
The compounds described in the above-mentioned U.S. patent specifications are low-molecular weight compounds and hence if such a compound is used individually it is deposited in crystalline form which results in lowering the mechanical strength of the image obtained and making long press runs difficult to attain. Accordingly, a resin such as a phenolformaldehyde resin, shellac or styrene-maleic anhydride resin is used as a carrier for the compound to prevent the light-sensitive layer from crystallizing and to compensate for any weakening of the mechanical strength. However, if materials other than a light-sensitive agent are incorporated into the light-sensitive layer there is a tendency to reduce the sharpness of the light-sensitive layer to development. In order to overcome such a difficulty, it is disclosed in U.S. pat. No. 3,046,120 that the light-sensitive agent itself is converted into a high molecular weight compound. However, if an aluminum plate is used as a support, the adhesive property of the compound described in the specification of the above U.S. patent with the aluminum is low, which results in reducing the mechanical strength of the image, and hence the practical value of such a plate is low.
Therefore, an object of the present invention is to provide a light-sensitive lithographic printing plate containing an improved light-sensitive agent unaccompanied by the abovementioned drawbacks. Other objects of this invention are to form a coating having sufficient film strength without the necessity of adding other film-forming agents as well as to increase the adhesive property between an aluminum plate and the coating thereon. A further object is to provide a sensitizer capable of being converted to a high molecular state and at the same time having a good film-forming capability.
The thereby produced photosensitive resin effectively serves as both the photosensitive component and the binder resin simultaneously without requiring the use of additional binding resins.